This application is based upon and claims priority from prior Italian Patent Application No. MI2000A002611, filed Dec. 4, 2000, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a driving circuit for electronically switched motors, particularly for brushless DC motors and switched reluctance motors.
2. Description of Related Art
In a conventional electronically switched motor, phase windings or poles are present on the stator but there are not windings on the rotor.
It is known that in a motor a magnetic attraction/repulsion force is generated between the rotor and the stator poles, when they approach themselves.
In this way current pulses, synchronized with the rotor revolution, can be provided by a driving circuit that makes full use of a current or voltage switching device, placed in series with each phase, as for example a thyristor or a transistor.
Every time the phase of an electronically switched motor is switched by the turning on of a transistor, in the driving circuit the current flows in the windings of a stator coming from a DC supply. A part of this energy is converted into mechanical energy causing the rotation of the rotor. Another part of the energy is stored in a magnetic field that is lost.
A typology of motor driving converters for recovering the lost energy is that known as C-dump, thanks to which some drawbacks, present in the unipolar converters for electronically controlled motors, such as the top sustainable power (at the maximum P=100 W) and the need for a double supply for application at high rotation velocity, have been overcome.
However the present C-dump converters have still some drawbacks such as the need for having drivers connected in high side configuration so as to control the switching of the switch dump and the need for including a passive or active filter so as to have the possibility of increasing the power factor.
The drivers connected in high side configuration require for their working either an isolated power supply or a charge pump circuit. This increases the cost and the complexity preventing the integration in a single chip.
In fact, particularly for this last aspect, that is for the correction of the power factor, usually a power active converter PFC (Power Factor Correction) is used.
However, proceeding in this way further semiconductor power devices and passive circuit elements are introduced which bring an increase in the manufacturing costs of the driving system.
One conventional technique for the manufacturing of a converter for electronically switched motors is shown in U.S. Pat. No. 6,014,001, in which some switches or high voltage drives placed in high side configuration are used.
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a driving circuit that is able to increase the performance of electronically controlled motors and to reduce the complexity and the costs of the driving circuit thereof.
According to preferred embodiments of the present invention, there is provided a driving circuit for electronically switched motors that includes a supply voltage rectifying stage, adapted to provide a rectified supply voltage, first switching means adapted to change their condition at the receiving of a predetermined electrical signal provided by a first control block, magnetic means adapted to provide a magnetic flux according to the condition of the first switching means, a plurality of transmission diodes, adapted to transmit an exciting current that flows through the magnetic means in first energy storing means adapted to store the exciting current flowing through the plurality of diodes, an energy return stage adapted to transfer the stored energy in the first energy storing means to the rectifying stage, and energetic conversion means adapted to receive the energy stored in the energy storing means through second switching means controlled by a predetermined electrical signal provided by a second control block, so as to provide a current as sinusoidal as possible.
Another object of the present invention is to make it easier to make a converter.
A further object of the present invention is to make it possible to integrate the power transistors on a single chip, reducing dimensions and costs.
Yet another object of the present invention is to make it unnecessary to add a passive or active filter with the C-dump converter.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.